The range of light intensities occurring naturally or man-made are very great and often exceed the useable dynamic range of optical devices used to observe a scene. For example, a camera may be used to view a scene with local bright spots several orders of magnitude brighter than the surrounding area. The light-sensitive area of the camera may have a linear dynamic range of one or two orders of magnitude which is its useable range. Light intensity variations below this range are not discernable because there is insufficient light to be detected. Light intensity variations above this range are not discernable because the detection device saturates. The present invention provides a method to extend the dynamic range of optical devices.
A particular area of application of the invention is in 3-D measurement. When using projected light to illuminate an object to be measured, it is sometimes necessary to control the amount of illumination to cause the reflected light intensity to be within the proportional region of the light-sensitive detector signal range. It is difficult to correlate the light intensity adjustment required at a received pixel with the projected ray that produced the reflected light. Also, adjustments made in the projector often must operate at high energy levels, where the present invention can operate more simply at the lower received light levels.